SATHEE: current-electricity Question 51

current-electricity Question 51

Question: Q. 4. Following circuit was set up in a meter bridge experiment to determine the value $X$ of an unknown resistance.

(a) Write the formula to be used for finding $X$ from the observations.

(b) If the resistance $R$ is increased, what will happen to balancing length? R&U [CBSE SQP 2018-19]

Sol. (a) $X = (100 - l) R / l$

(b) Balancing length will increase in increase of resistance $R$ .

[CBSE Marking Scheme 2018]

Q. 5. In a potentiometer arrangement for determining the emf of a cell, the balance point of the cell in open circuit is $350 cm$ . When a resistance of $9 Ω$ is used in the external circuit of the cell, the balance point shifts to $300 cm$ . Determine the internal resistance of the cell.

A [ Delhi & O.D. 2018] Sol. Stating the formula 1

Calculating $r$

We have, $r = (\frac{l_{1}}{l_{2}} - 1) R = (\frac{l_{1} - l_{2}}{l_{2}}) R 1$

$∴ r = (\frac{350 - 300}{300}) \times 9 Ω$

$= \frac{50}{300} \times 9 Ω = 1.5 Ω$

$1 / 2$

[CBSE Marking Scheme, 2018]

Short Answer Type Questions-II

Q. 1. (i) Write the principle of working of a metre bridge.

(ii) In a metre bridge, the balance point is found at a distance $l_{1}$ with resistances $R$ and $S$ as shown in the figure.

An unknown resistance $X$ is now connected in parallel to the resistance $S$ and the balance point is found at a distance $l_{2}$ . Obtain a formula for $X$ in terms of $l_{1}, l_{2}$ and $S$ .

A [O.D. I, II, III 2017]

Show Answer

Solution:

Ans. (i) Principle of metre bridge

(ii) Relation between $I_{1}, I_{2}$ , and $S$

(i) The principle of working of a metre bridge is same as that of a balanced Wheatstone bridge.

Alternatively

When $i_{G} = 0$ , then $\frac{P}{Q} = \frac{R}{S} 1 / 2$

(ii)

$\frac{R}{S} = \frac{l_{1}}{100 - l_{1}}$

$1 / 2$

When $X$ is connected in parallel :

$\frac{R}{(\frac{X S}{X + S})} = \frac{l_{2}}{100 - l_{2}}$

On solving we get, $X = \frac{l_{1} S (100 - l_{2})}{100 (l_{2} - l_{1})}$

[CBSE Marking Scheme 2017]

Ans. (i)

Princeple of workeng of a metec beidge

The pecncipce is Wheatsen principce

If foce eescisances $D, Q, R$ ands aeconneded

in the whealstone beidge in the foclowing

manner, then at balanced condction, 2 cuerenc

in the galvanomelice is $2 e x 0$ on the

lescseance can be fornd:

(ii)

[II Q. 2. Draw a circuit diagram of a potentiometer. State its working principle. Derive the necessary formula to describe how it is used to compare the emfs of the two cells.

DiO.D. I, II, III 2015]

Ans. The circuit diagram of the potentiometer, is as shown here:

Working Principle :

The potential drop, $V$ , across a length $l$ of a uniform wire, is proportional to the length $l$ of the wire. $1 / 2$ or, $V \propto l$ (for a uniform wire) Derivation : From the figure, connect points 1 and 3 together with balance point at point $N_{1}$ where $A N_{1} = l_{1}$ Now connect points 2 and 3 together with balance point at point $N_{2}$ where $\mathrm{AN}{2}=l{2} $.$ 1 / 2$ We have,

So,

and

$E_{1} = k l_{1}$ $E_{2} = k l_{2}$

$\frac{E_{1}}{E_{2}} = \frac{l_{1}}{l_{2}}$

$1 / 2$

Current Electricity

current-electricity Question 51

Short Answer Type Questions-II

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Engineering Preparation

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Current Electricity

current-electricity Question 51

Short Answer Type Questions-II

Table of Contents

Engineering Preparation

Medical Preparation

NCERT Books & Solutions

Important Resources

Other Resources

Syllabus

Test Platform

Sample Mock Test

Mentorship

NCERT Exercise Video Solution

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